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RC submarine lateral stabilization structure

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  • RC submarine lateral stabilization structure

    We know that when the rc submarine or ship model is on the water, it will be disturbed by wind or wave currents, which will directly lead to instability of the model. Today's topic is how to enhance the lateral stability of a submarine and use a very simple method so that more people can actually do it. In fact, there are many ways to increase the lateral stability of rc ships, and one effective way is to use a momentum wheel system to bring the ship to a dynamic and stable equilibrium based on the conservation of angular momentum and the tuning of the PID algorithm. But this is not the method I will discuss today. Today I will propose a simpler means to increase the lateral stability of a submarine. We all know that WWII submarines are easily unstable on the surface because of their slender hulls, so builders added a pair or even more pairs of bilge keels to the bottom of the submarine to increase the stability of the submarine. Nowadays, can we also increase the stability of a submarine (without changing the appearance of the submarine) by adding bilge keels? So, we can add bilge keels to the interior of the submarine hull, if not scientifically calculated, the bilge keels are at a 45 degree angle to the horizontal line and are connected to the bulkheads. The reason for this design is also simple, because we use wet hull structure, the whole WTC is submerged in water, when the submarine produces lateral roll (whether the submarine is stationary in water or in motion), the water inside the hull is stationary with respect to the bilge keel inside, while the bilge keel is swaying from side to side (in motion), so in such a reference system, the bilge keel is effective, because The stationary water dampens the moving bilge keel and by doing so increases the stability of the submarine. Here's a diagram that clearly shows what I think.

    V

    Click image for larger version

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  • #2
    What you're describing is more of an internal baffle.

    Click image for larger version

Name:	images (12).jpeg
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ID:	162802 A bilge keel is a nautical device used to reduce a ship's tendency to roll. Employed in pairs, one for each side of the ship bilge keels increase hydrodynamic resistance to rolling, making the ship roll less ( wikipedia)

    Just use keel weights. Simple.
    Make it simple, make strong, make it work!

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    • #3
      I have a large OTW S Class WWII boat. I had a great conversation with the builder who talked about the difficulties in trimming that boat. He said much of the issue was free-surface effect caused by the large amount of water captured inside the scale hull but, obviously, outside the WTC. It makes sense that this would be a problem possibly with roll but definitely in the pitch axis.

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      • #4
        Originally posted by redboat219 View Post
        What you're describing is more of an internal baffle.

        Click image for larger version  Name:	images (12).jpeg Views:	0 Size:	6.7 KB ID:	162802 A bilge keel is a nautical device used to reduce a ship's tendency to roll. Employed in pairs, one for each side of the ship bilge keels increase hydrodynamic resistance to rolling, making the ship roll less ( wikipedia)

        Just use keel weights. Simple.
        Keel weights are essential, but such the condition in which you utilize the keel weights and still couldn't make the sub (probably a WW2 type) stable when running on the surface with the disturbance of wind and wave currents,what will you do next? More foams and weights make the sub heavier,actually it's your own choice to use different methods which are suitable for your sub. BTW, internal bilge keels are not as complicated as you think to build, they could be part of your 3D printed hull or you just make them via resin casting.

        V
        Last edited by Sam Victory; 07-10-2022, 06:35 PM.

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        • #5
          Brilliant!... It has to work. The ideal thing would be to make it part of the cradle system that holds the WTC/ sub driver.

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          • #6
            This feels like there is a bit of overthinking going on here. For the beginners out there, just remember: "Weight goes low. Foam goes high." Putting two bilge keels inside the hull at 45 degrees to one another is not as effective as a single internal keel placed at the lowest point. This is simple physics. The weight needs as long a moment arm as possible from the centerline of the boat. Putting the weight at 45 degrees halves that distance, in effect halving the ballast effectiveness at maintaining static stability.

            External keels can help reduce the effect of wind-induced roll as they become more of an aerofoil, resisting water movement perpendicular to their length.

            In practical application, in the scale we are building our boats at, I see no need to add a non-scale external keel to our boats. Their effectiveness (unless grossly oversized) is negligible.

            Just my two cents.


            Bob

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            • #7
              Hi,Bob!Maybe my drawing is not very standard, we should focus on the center of gravity of the submarine rather than the center point. The ballast lead is placed at the lowest point, so the center of gravity of the submarine is very low, and the bottom force arm of the submarine is relatively short, of course you have to depend on the specific shape of the boat. Perhaps I am complicating something simple, but adding internal bilge keels does not make maintenance difficult and does not take up much space, but has the benefit of providing "extra" stability to the submarine.

              In fact, some sailboats do have the rocker panels mounted perpendicular to the bottom, but more often they are mounted in the bilge of the hull. Indeed, just simple physics. Why is it mounted in the bilge instead of on the bottom or the side of the boat? As early as more than a hundred years ago, people have installed bilge keel on the side, bilge and bottom of the ship to test, and the test shows that the bilge keel installed in the bilge has the best effect to reduce the shaking. The analysis reason is that the bilge is farthest from the ship's center of gravity G, the curvature of the bilge is large, the flow velocity here is larger, so the damping moment caused by the bilge keel is improved. Another factor that has an effect on the rocking reduction effect is the size of the bilge keel. First, the width of the bilge keel has an effect on its damping effect. Because the additional damping caused by bilge keel increases with the width, and the second is the effect of length on the effect of rocking reduction, but because of the different types of ships, there is an effective value of the length. When the effective value is exceeded and the length is increased, the bilge keel efficiency does not change much, because the bilge keel against the bow and stern is in the position where the curvature of the bilge is reduced, so the damping moment is very small.

              V
              Last edited by Sam Victory; 07-11-2022, 07:44 AM.

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              • #8
                I don’t think internal bilge keels will be very effective for model subs. When I was operating my U-boat, the smallest wave on the lake has such big momentum compared to the scale of our models, that in addition to the wind, is enough to make the model sway from side to side no matter how much weight is in the keel. I have my foam up high and ballast in the keel like Bob said, and even with that setup the model still rolls.

                Nate

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                • #9
                  Hi, Nate! I accept your criticism, but I'm afraid you can't judge a theory without a basis. Not to mention that it's a theory that has been proven correct for a long time. My personal understanding of the rc model is that the rc model is a reflection of those big real things that are related and similar in some way. So the basic theory is connected. Maybe it is possible that adding internal bilge keel is not very effective, but the teachers in school told us how to prove things right: first have a conjecture, then design an experiment to prove it. Applying the theory to practice, and just talking without doing is useless! Finally come to a conclusion. With this in mind, I did a simple experiment. Since I had just returned from the lab, I didn't have the better tools to do it. So I used a plastic bottle with a weight mounted on the bottom and put it into water ballasted to the set water line. Then I used my hand to make the bottle shake from side to side until the bottle was stable, calculating the stability time several times to 7 to 8 seconds or even longer. Then I put cardboard on both sides of the bottle to simulate the bilge keel, and after the same operation, the stabilization time was 3 to 4 seconds. In fact this is very correct theory and I don't think it is necessary to practice it anymore, maybe it is better by mathematical modeling. But I still did the experiment and came up with the results....


                  V

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                  • #10
                    My suggestion would be to actually build a working RC submarine and experiment with it yourself. External bilge keels are one thing, but often inside the wet space of a submarine hull, the radial space between the WTC and the inner hull is often very limited, unless you use a very thin WTC diameter. There are also other factors at work within a wet hull sub that you haven’t considered, such as foam placement, location of bulkheads, WTC mounts, etc. Theory is one thing, but actual practical application is another.

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                    • #11
                      As I mentioned before, the internal bilge keel wouldn't take too much space, and they are connected to the bulkheads which should be part of the hull. Actually , if I GOT enough time , I will certainly made a rc sub and show it to all you guys. As far as I concerned, the only thing I could do is to share the control theory or other knowledge I have learned to the realm of rc subs. Perhaps people ,the modelers like you ,could have a try.

                      V

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                      • #12
                        Sam, Build some mock-ups and test. I want to see the results. It is an interesting idea. Not that many have a need, especially beginners, but I would like to see if it is effective. Right now it is a drawing and nothing more than a good idea. The proof is in the finished product. Thanks for sharing.

                        If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

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                        • #13
                          Actually, if someone could 3D print the Gotland class found here, it already has the 45 degree internal baffle structure integrated in the model:

                          https://cults3d.com/en/3d-model/game...s-gotland-1-48

                          Adding some weights to the baffles would be an easy way to test the stability in rough waters.

                          Nate

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                          • #14
                            Actually, if someone could 3D print the Gotland class on Cults3D, it already has the 45 degree internal baffle structure integrated in the model. Adding some weights to the baffles would be an easy way to test the stability in rough waters.

                            Comment


                            • #15
                              When I have time, I will definitely try it, just may be a long time from now. Just because I don't have enough time, I'm hoping that other members of the forum can apply my ideas in a practical way.

                              Sincerely
                              V

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